Recently, in the field of wireless communication, an MIMO (Multiple Input Multiple Output) is featured. The MIMO enables increase in the transmission rate without spreading the frequency band width by transmitting a signal from a wireless transmission device to a wireless reception device using same frequency and the same timing. In the MIMO system, the wireless reception device requires method of separating transmission signals which are spatial multiplexed, because the wireless reception device receives different multiplexed transmission signals.
FIG. 19 is an explanation diagram of a conventional MIMO system. A wireless transmission device 51 includes M (M is integral number which is 2 or greater than 2) number of transmission antennas. The wireless transmission device 51 transmits different transmission signals s1 to sM from each of the transmission antennas As1 to AsM to a wireless reception device 52. The transmission signals s1 to sM which were transmitted from the each of the transmission antennas As1 to AsM of the wireless transmission device 51 are received by N (N is integral number which is 2 or greater than 2) number of reception antennas Ar1 to ArN of the wireless reception device 52. In this case, transmission and reception signals of the MIMO system are represented by formulas (1) to (5) which are shown below.r=Hs+n  (Formula 1)r=[r1 . . . rN]T  (Formula 2)
                    H        =                  (                                                                      h                  11                                                            …                                                              h                                      1                    ⁢                    M                                                                                                      ⋮                                            ⋱                                            ⋮                                                                                      h                                      N                    ⁢                                                                                  ⁢                    1                                                                              …                                                              h                  NM                                                              )                                    (                  Formula          ⁢                                          ⁢          3                )            s=[s1 . . . sM]T  (Formula 4)n=[n1 . . . nN]T  (Formula 5)
The vector r of a left part of the formula (1) and a left part of the formula (2) are N-row by 1-column reception signal vectors which have elements of reception signals which are received by each of the reception antennas Ar1 to ArN of the wireless reception device 52. The vector H of a left part of the formula (3) is an N-row by M-column channel matrix which has elements of channel responses (h11 . . . hN1, . . . h1M . . . hNM) between each of the transmission antennas As1 to AsM of the wireless transmission device 51 and the reception antennas Ar1 to ArN of the wireless reception device 52. The h11 is a channel response between the transmission antenna As1 and the reception antenna Ar1. hN1 is a channel response between the transmission antenna As1 and the reception antenna ArN. h1M is a channel response between the transmission antenna AsM and the reception antenna Ar1. hNM is a channel response between the transmission antenna AsM and the reception antenna ArM. The symbol “T” in the top right of matrix indicates that the matrix is transposed matrix.
The vector s of a left part of the formula (4) is an M-row by 1-column vector which has elements of transmission signals which are transmitted by each of the transmission antennas As1 to AsM of the wireless transmission device 51. The vector n of a left part of the formula (5) is N-row by 1-column noise vector which has elements of noise which are added at each of the reception antennas Ar1 to ArN of the wireless reception device 52.
As a technique which departs spatial multiplexed signals like formula (1), linear processes (for example, the ZFD (the Zero Forcing Detection) and the MMSED (the Minimum Mean Square Error Detection) are known. These linear process are frequently used, because the number of calculation is fewer. The aforementioned MIMO system is disclosed in Non Patent Document 1.    Non Patent Document 1: D. Gesbert, M. Shafi, D. Shiu, P. J. Smith, A. Naguib, “From Theory to Practice: an overview of MIMO space-time coded wireless systems”, IEEE JSAC, April, 2003